a) Field of the Invention
The present invention relates to a semiconductor device and more particularly to a MOS type semiconductor device with salicide electrodes.
b) Description of the Related Art
As the integration degree of semiconductor integrated circuit devices is becoming high, MOS transistor elements of these devices are scaled down and becoming progressively smaller.
A gate length, for example, has been shortened from sub-micron to half-micron, and has a tendency to further be shortened to 0.35 .mu.m, 0.25 .mu.m, and even to 0.1 .mu.m. The shorter the gate length, the more a high speed operation becomes advantageous. A resistance of a gate electrode is required to be suppressed low even if it is made narrow.
As electrode materials having a low contact resistance to a silicon surface, there are known metal silicides containing Ti, Pt, Co, or other metals. These metal silicides have a low sheet resistance at the interface to silicon, and are suitable for the connection of MOS transistors to wirings such as Al wirings.
Most gate electrodes of MOS transistors use silicon materials such as polycrystalline silicon and amorphous silicon. With a silicon gate electrode, the materials of the source, gate, and drain are all silicon. If a salicide (self-aligned silicide) process is used, contacts can be formed at these silicon regions. In order to make a MOS transistor small, it is necessary to reduce the area of the source/drain regions.
As MOS transistors are becoming small, it is required to form good contacts to small areas of silicon. In addition, as transistors are scaled down, it is necessary not only to shorten gate lengths but also to shallow the source/drain regions in order to avoid a short channel effect.
For example, the depth of source/drain regions is about 150 to 200 nm for a gate length of 0.35 to 0.5 .mu.m, about 100 nm for a gate length of 0.25 .mu.m, and about 80 nm for a gate length of 0.15 .mu.m.
With such small transistors, good contacts are not always formed on silicon by conventional contact forming techniques.